1. Field of the Invention
The present invention relates to a flame retardant hydraulic oil to be used in rolling mills, die casting machines and the like in the field of the steel making industry and the nonferrous metal industry and in hydraulic instruments and the like in the construction industry. More particularly, it relates to a flame retardant hydraulic oil excellent in the flame retardancy, heat stability and oxidative stability, unaccompanied by the dangers of pinhole fire at sites of use and giving rise to no environmental contamination.
2. Description of the Related Arts
Generally, it is essential that the flame retardant hydraulic oils have the following characteristics:
(1) the oils are excellent in viscosity-temperature properties to ensure the transmission of pressure and power,
(2) the oils have appropriate viscosities to minimize the loss of pressure and power,
(3) the oils are excellent in the heat stability, oxidative stability and lubricity to provide the longer service life,
(4) the oils are excellent in the demulsibility to protect from the possible mixture of water, and
(5) the oils have flash points high enough not to permit the continuous burning even if the oils are ignited, since it is quite likely that the oils are used where there are the high risks of fire.
As these flame retardant hydraulic oils, there have been conventionally used those of emulsion series, those of water-glycol series, those of phosphoric acid ester series, those of fatty acid ester series and the like.
However, the hydraulic oils of emulsion series and those of water-glycol series are low in heat stability, oxidative stability, and lubricity or are difficult to dispose of with waste water.
Furthermore, the hydraulic oils of phosphoric acid ester series have shortcomings in that their viscosity-temperature properties and hydrolytic resistance are deficient, the oils are responsible for the deterioration of seal materials and the exfoliation of coats. Also it is difficult to dispose of waste oils containing such hydraulic oils by burning.
On the other hand, the hydraulic oils of fatty acid ester series are good on the above-mentioned points, having found their application in wide segments of market. But these oils are deficient in the fire resistance and flame retardancy. Various studies have been conducted in an attempt to overcome these problems incidental to the hydraulic oils of fatty acid ester series. In fact, the technique covering the flame retardant oils of fatty acid ester series has been disclosed, for example in Japanese Patent Applications Laid Open No. 18467/1980, No. 226096/1984, No. 125598/1988, No. 214795/1990 and No. 21697/ 1991.
However, all of flame retardant hydraulic oils disclosed in said patent applications have the flame retardancy defined only in terms of flash point. The most important problem of flame retardant hydraulic oils is accidents to be caused by pinhole fire. Specifically, the flame retardant hydraulic oils should have the properties that the oils are hard to catch fire even if the oils are erupted from pinholes and, even in the case of catching fire, do not permit it to develop into the continuous burning if the source of fire is removed. These properties cannot be obtained merely by having the high flash points.
The present inventors have taken note of the properties of continuous burning and conducted the studies by spraying and burning various flame retardant oils under high pressure. The studies have resulted in finding that conventional flame retardant oils of fatty acid ester series (particularly the fatty acid esters made of the oleic acid only) do not have the sufficiently satisfactory flame retardancy, although these oils are highly spoken of as flame retardant.
Thus, the present inventors have made the further intensive studies with a view to developing a flame retardant hydraulic oil of fatty acid ester series free from the properties of continuous burning and excellent in the heat stability, oxidative stability and fluidity. As the results, it has been found that the desired flame retardant hydraulic oil can be obtained by incorporating a fatty acid ester which is formed by reacting a specific polyol with an oleic acid and a isostearic acid or with the oleic acid, the isostearic acid and another monocarboxylic acid in a specific ratio. The present invention has been completed on the basis of this finding.
Accordingly, an object of the present invention is to provide a flame retardant hydraulic oil containing a hydraulic base oil comprising as the essential component a synthetic ester, which is a product formed by reacting (A) at least one polyol selected from the group consisting of neopentyl glycol, 2,2-dimethyl-3-hydroxypropyl-2xe2x80x2,2xe2x80x2-dimethyl-3xe2x80x2-hydroxypropionate, glycerin and trimethylolpropane with (B) a carboxylic acid comprising 15 to 85% by mole of oleic acid based on the total carboxylic acid and 15 to 85% by mole of isostearic acid based on the total carboxylic acid or a carboxylic acid obtained by incorporating into said carboxylic acid 85% by mole or less of monocarboxylic acid having 6 to 22 carbon atoms (provided that the oleic acids and isostearic acids are excluded) based on the total carboxylic acid, said synthetic ester having a kinematic viscosity of 40 to 80 cSt at 40xc2x0 C. and a flash point of 290xc2x0 C. or higher.
The present invention will be described in greater detail hereinafter:
The flame retardant hydraulic oils of the present invention use a hydraulic base oil comprising a fatty acid ester as the essential component. The fatty acid esters of the present invention are a synthetic ester obtained by reacting a polyol of Component (A) with an oleic acid and an isostearic acid of Component (B), or by reacting a polyol of Component (A) with an oleic acid, isostearic acid and a monocarboxylic acid having 6 to 22 carbon atoms (provided that oleic acids and isostearic acids are excluded) of Component (B).
The polyols of Component (A), which are used in the reaction to form the synthetic esters are at least one polyol selected from the group consisting of neopentyl glycol, 2,2-dimethyl-3-hydroxypropyl-2xe2x80x2,2xe2x80x2-dimethyl-3xe2x80x2-hydroxypropionate, glycerin and trimethylolpropane. These polyols can be used singly or in their two or more mixture.
On the other hand, the carboxylic acids of Component (B) which are used in the reaction to form the synthetic esters are a carboxylic acid comprising an oleic acid and an isostearic acid as the essential component and further preferably a monocarboxylic acid having 6 to 22 carbon atoms, provided that the oleic acids and isostearic acids are excluded.
Upon their esterification with the polyols of Component (A), the carboxylic acids of Component (B) comprise the oleic acids in a ratio of 15 to 85% by mole to the total carboxylic acid, the isostearic acid in a ratio of 15 to 85% by mole to the total carboxylic acid and the monocarboxylic acid having 6 to 22 carbon atoms in a ratio of 85% by mole or less, preferably 70% by mole or less to the total carboxylic acid, if said monocarboxylic acids are put to use.
If the ratio of the oleic acids in the carboxylic acids is less than 15% by mole, the low fluidity would undesirably result. If it is more than 85% by mole, the flame retardancy would be undesirably deficient. Furthermore, if the ratio of the isostearic acids is less than 15% by mole, the flame retardancy would be undesirably deficient. If it is more than 85% by mole, the fluidity would be undesirably at a low side.
The monocarboxylic acids having 6 to 22 carbon atoms are not particularly limited. Their examples include a straight chain saturated fatty acid such as caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachic acid and behenic acid; a straight chain unsaturated fatty acid such as undecenoic acid, elaidic acid, cetoleic acid, erucic acid and brassidic acid; and a branched chain saturated fatty acid such as isomyristic acid, isopalmitic acid, 2,2-dimethylbutanoic acid, 2,2-dimethylpentanoic acid, 2,2-dimethyloctanoic acid, 2-ethyl-2,3,3-trimethylbutanoic acid, 2,2,3,4-tetramethylpentanoic acid, 2,5,5-trimethyl-2-t-butylhexanoic acid, 2,3,3-trimethyl-2-ethylbutanoic acid, 2,3-dimethyl-2-isopropylbutanoic acid, 3,5,5-trimethylhexanoic acid and 2-ethylhexanoic acid. These monocarboxylic acids can be used singly or in a mixture.
With respect to the flame retardant hydraulic oils of the present invention, the hydraulic base oils comprise as the essential component the synthetic esters formed by the ordinary esterification or the transesterification of polyols of Component (A) to carboxylic acids of Component (B).
In the processes wherein the polyols of Component (A) and the carboxylic acids of Component (B) are subjected to the esterification or transesterification, the ratio of the charge of Component (A) to that of Component (B) can be adjusted to obtain the viscosity as desired. Furthermore, it is preferable to remove a fraction of light components to perfection, to provide the flash point of 290xc2x0 C. or higher.
The thus obtained synthetic esters can be used singly or by mixing the esters to have the viscosity as desired, to serve as the hydraulic base oil.
According to the present invention, the synthetic esters to be used as the hydraulic base oil have the kinematic viscosity of 40 to 80 cSt, preferably 45 to 65 cSt at 40xc2x0 C. If the viscosity is too high, the low fluidity would result, followed by low efficiency of instruments. If the viscosity is too low, the hydraulic oils are liable to change into a mist and burn when the oils are erupted. It is preferable that the hydraulic oils have the flash point of 290xc2x0 C. or higher. If the flash point is lower than 290xc2x0 C., the hydraulic oils are liable to catch fire.
Furthermore, it is preferable that the hydraulic oiles have the iodine value of 65 or lower. The oxidative stability can be shown by such iodine value. Therefore, if the value is higher than 65, the hydraulic oiles are liable to have a larger amount of olefin component and shorter oxidation life, and to burn.
The flame retardant hydraulic oils of the present invention contain the hydraulic base oils comprising the thus obtained synthetic esters as the essential component. Furthermore, it is preferable that said flame retardant hydraulic oils additionally contain a high-molecular compound having a number average molecular weight of 10,000 to 400,000. As the high molecular compound, a polyolefin, a polyacrylate, a polymethacrylate, a polyalkylene glycol, a polyalkylene glycol alkylether, a styrene-olefin copolymer, a styrene-maleic acid ester copolymer, a polyester and the like can be mentioned. Particularly, the methacrylate-based polymers or the styrene-maleic acid ester copolymers are preferably used.
The base oils are made less liable to change into a mist and it is said high molecular compounds which are added thereto so that the mists of base oils are even harder to develop. From this viewpoint, their molecular weights are preferably 10,000 to 400,000. If the molecular weight is smaller than this range, said effect can hardly be obtained undesirably If it is larger than the range, the hydraulic oils are undesirably liable to deteriorate due to the shear when the oils are used, followed by the fadeout of effects and the reduction of viscosity.
In the present invention, it is preferable that said high molecular compounds be contained in the hydraulic oils in a ratio of 0.01 to 2.0% by weight. If the content is smaller than this range, the present invention is hardly effective. If it is larger than this range, the hydraulic oils are more liable to deteriorate due to shear undesirably.
If necessary, the flame retardant hydraulic oils of the present invention may as well be mixed with routinely used lubricating oil additives, such as antioxidant, extreme pressure agent, rust preventives, defoaming agent, demulsifier and the like.
Examples of the antioxidant to be used herein include a phenol-based antioxidant such as 2,6-di-t-butyl-4-methylphenol, 4,4xe2x80x2-methylenebis(2,6-di-t-butyl-4-methylphenol; an amine-based antioxidant such as N-phenyl-xcex1-naphthylamine, N-phenyl-xcex2-naphthylamine, phenothiazine and monooctyldiphenylamine; or a sulfur-based antioxidant such as alkyl disulfide and benzothiazole; and a zinc dialkyldithiophosphate.
Examples of the extreme pressure agent include a zinc dialkyldithiophosphate, a dialkylpolysulfide, a triarylphosphate, a trialkylphosphate and the like.
Examples of the rust preventives include an alkenyl succinate, a sorbitan monooleate, a pentaerythritol monooleate and an aminephosphate.
Examples of the defoaming agent include a dimethylpolysiloxane and a diethylsilicate. Examples of the demulsifier include a polyoxyalkylene glycol, a polyoxyalkylene alkylether, a polyoxyalkylene alkylamide and a polyoxyalkylene fatty acid ester.
It is preferable that the flame retardant hydraulic oils of the present invention as obtained above have the biodegradability of 67% or more as the result of the biodegradation test according to the CEC method.
Obtained as above, the flame retardant hydraulic oils of the present invention are excellent in the flame retardancy, heat stability, oxidative stability and unaccompanied by the dangers of pinhole fire by incorporating the hydraulic base oils which comprise as the essential component the synthetic esters formed by reacting the polyols of Component (A) with the carboxylic acids of Component (B).
Therefore, these flame retardant hydraulic oils can find their application, for example in various hydraulic instruments, construction equipment, injection machines, machine tools, hydraulically driven robots and the like. Furthermore, they can be used as an engine oil, a gear oil, an industrial lubricating oil for other uses and the like.
Moreover, the oils are biodegradable, capable of finding the application as a lubricating oil preferable from the viewpoint of environmental protection.